Systematic ultrasound identification of the dorsal scapular and long thoracic nerves during interscalene block

Background and Objectives: The use of ultrasound for in-plane interscalene block shifts needle insertion to a more posterior approach through the middle scalene muscle, when compared with classic nerve stimulator techniques. Branches from the brachial plexus, including the dorsal scapular and long thoracic nerves, are often anatomically located within the middle scalene muscle. The aim of this study was to use ultrasound to identify and characterize the frequency and position of the dorsal scapular and long thoracic nerves located in the middle scalene muscle. Methods: We recruited 50 subjects who presented for shoulder surgery. Before block placement, ultrasound was used to evaluate the area posterior to the brachial plexus for visible segments of the long thoracic and dorsal scapular nerves. If nerves were identified, a stimulating Tuohy needle was advanced in close proximity. Current was then applied through the needle, and motor response confirmed the visualized nerve as being either the dorsal scapular nerve or long thoracic nerve. Results: Ninety percent of the subjects had a nerve visible under ultrasound assessment within or superficial to the middle scalene muscle. The nerves were located at similar depth as the perceived C6 nerve root, at 1.1 ± 0.4 cm from skin and 0.7 ± 0.4 cm posterior from the brachial plexus. Stimulation revealed that the nerve identified on ultrasound was the dorsal scapular nerve (77%) or the long thoracic nerve (23%). Conclusions: This descriptive study revealed that the dorsal scapular and long thoracic nerves routinely could be identified with ultrasound.